1,721,354 research outputs found
Replication Data for: Thermal evolution of life history and heat tolerance during range expansions toward warmer and cooler regions
No full textPhenotype data of the experiment described in Carbonell & Stoks. 2020. Ecology. The purpose was to test for evolution of phenotypes of the damselfly Ischnura elegans during range expansion from France into two regions in Spain (northern Spain and Southern Spain). The datasets contain values of measured variables at the end of a rearing experiment from the egg stage of larvae from the three regions reared at 4 temperatures. Measured variables are the following: heat tolerance (CTmax), development time, food intake, growth rate, growth efficiency, and survival
Multivariate seksuele selectie op kenmerken gerelateerd met performantie in niet-territoriale en territoriale waterjuffers ,,
No full textSexual selection is a powerful force directing evolution which can vary in strength (strong or weak), direction (positive or negative) and form (linear or nonlinear). Despite the many studies on sexual selection, three aspects remain understudied, yet very relevant to fully understand sexual selection on the traits of a given species. (1) While most of the studies on sexual selection focused on a single or few phenotypic traits, a minority of studies followed a multivariate approach. This is important to disentangle direct selection versus indirect sexual selection on a trait. (2) Most studies focused on morphological traits (mainly body size) and ignored physiological traits, for example related to energy reserves, and locomotor performance. (3) Finally, recent studies suggest that sexual selection may vary both among populations and among time periods within a given population. Paying attention to such spatiotemporal variation in sexual selection will learn whether the same traits are preferred across populations and seasons which is directly relevant to understand the evolutionary dynamics of these traits.
To study these aspects in-depth we used damselflies, upcoming model systems in ecology and evolution. In this thesis we combined field and laboratory studies to obtain a multivariate picture of sexual selection on whole-organism performance and the underlying morphological and physiological traits in the scrambling damselfly Coenagrion puella and the territorial damselfly Chalcolestes viridis. In addition, we performed a detailed morphometric analysis and reconstructed phylogenetic trees to resolve the position of C. viridis and its eastern form, C. parvidens.
1. The taxonomic position of C. viridis and C. parvidens
Our genetic data supported the genus status of Chalcolestes. We found that the two Chalcolestes taxa formed a monophyletic group separated from other investigated European Lestes species based on both the mitochondrial COI gene and the nuclear ribosomal ITS region. The morphometric study showed that C. viridis and C. parvidens were differentiated in morphometric space, even though there were no single morphometric characters that could conclusively distinguish the two taxa. Our genetic analysis further supported the species status of C. parvidens. The two Chalcolestes taxa do not share haplotypes, suggesting that lineage sorting was complete. Although we find the data supportive of recognizing C. parvidens as a distinct species, further detailed morphologic and genetic analyses are needed to shed further light on how both species are separated reproductively.
2. Spatial and temporal variation of sexual selection on whole-organism performance and the underlying morphological and physiological traits
Although the two study species have a contrasting mating system, we found that flight endurance had a key role determining mating success in both species. In contrast, we could not detect selection on flight speed in neither of the species. This indicates that flight speed is not as relevant as flight endurance neither for territorial defence nor for scrambling in the study species. This is intriguing as speed is likely to play a role in capturing the female, especially in scrambling species. More likely, speed is already maximized due to strong selection by other agents such as predators leaving less variation to detect selection on this performance trait, while endurance is less relevant for damselflies to escape predators. From the six key phenotypic traits, four were found to be under sexual selection. The detected selection patterns that could not be explained via their effect on flight performance are generating novel testable hypotheses about how the covariation between these traits and mating success was generated. This urges caution when using different traits as proxies for the two studied aspects of flight performance. We provided support that not only spatial but also temporal variation occurs within a single reproductive season for sexual selection on phenotypic traits. Furthermore, we provided the first test for spatially and temporally varying sexual selection on performance traits, which confirmed our novel hypothesis that selection on performance (here flight endurance) is more stable through space and time than the observed selection on the underlying traits. We hypothesize this to be a general pattern given that, compared to morphological and physiological traits, performance is the direct target of selection. In contrast, selection on phenotypic traits may be more variable as the contribution of phenotypic traits to performance may depend on environmental conditions. Additionally, different combinations of underlying morphological and physiological traits may result in similar performance.
The here reported studies are the first investigating sexual selection on flight performance and the underlying physiological and morphological traits in an aerial scrambling and territorial species. The PhD thesis adds to the increasing number of studies finding that the strength, direction, and form of selection are often spatially and temporally dynamic. This thesis helps to refine our knowledge of the spatial and temporal dynamics of selection patterns in nature, which is of paramount importance to arrive at a better understanding of adaptive evolutionary dynamics of traits in natural populations.status: Publishe
Het pace-of-life syndroom en global change-stressoren in waterjuffers ,,
No full textTo understand and predict patterns in trait variation along environmental gradients and in response to stressors, the integration of traits into suites of correlated traits or ‘syndromes’ has received increasing attention. Because of the presence of such syndromes, the plastic and evolutionary responses of organisms to selection pressures involve coordinated changes in many traits. A promising concept for the integration of traits is the pace-of-life syndrome (POLS) hypothesis, which predicts the integration of life-history, behavioural and physiological traits into a syndrome that varies along a fast-slow continuum. It predicts, for example, that fast-lived animals are characterised by fast growth, early reproduction, a short lifespan, fast metabolism, low investment in body maintenance (such as immune function) and proactive behaviours like high activity and boldness (as opposed to reactive behaviour). Furthermore, such fast-slow variation is expected to exist at different levels of biological organisation: between species, between populations within species and between individuals. In this thesis, I investigated whether there is support for the POLS, how it is affected by different stressors [ultraviolet radiation (UV), contaminants (zinc and the pesticide chlorpyrifos), warming], and whether it can be used to predict organisms’ sensitivity to stress. I did this in a series of common-garden experiments, using coenagrionid damselflies (Ischnura sp. and Coenagrion puella) as model organisms, exploiting the strong variation in life-history strategy linked with voltinism across latitudes and larval habitat types (pond permanence).
I found strong evidence for a fast-slow life-history continuum at all three levels of organisation. Ordering along this continuum at the interspecific and interpopulation level was tightly linked to differences in time constraints imposed by voltinism and larval hydroperiod. Behavioural traits were mostly found to cluster along a proactive-reactive axis, but only at the latitudinal level this was tightly coupled with the fast-slow life-history continuum. The lack of a strong link between life history and behaviour might partly be due to POLS-related patterns in digestive physiology, like conversion and assimilation efficiencies. Patterns in physiology were least in accordance with the predictions under the POLS hypothesis. Among individuals and across latitudes, there was some evidence for the integration of several physiological traits into a syndrome, but this was not consistently associated with a fast-slow continuum. This might be due to the diversity of physiological pathways, that might overlap in function or the existence of trade-offs at smaller trait scales (among two or more physiological traits) instead of trade-offs between pace and investment in body maintenance. In general, the existence of multidimensional trade-offs, where different combinations of traits may lead to a similar pace, might be an explanation for the overall limited integration of traits along a fast-slow axis here observed.
Contaminant exposure (zinc/chlorpyrifos) and warming strongly affected the patterns of covariation among traits at the within-population level. Contaminant exposure generally induced a stronger trait integration among behavioural traits and among physiological traits, indicating stronger trade-offs under energy-constraining conditions. Furthermore the contaminants and temperature treatments (alone and in combination) changed the higher-level associations between life-history, behavioural and physiological traits, leading to coupling, decoupling and inversion of trait associations. Whether these changes affect the fitness of individuals and scale up to impact population dynamics and community structure remain open questions and provide opportunities for future research.
In contrast with the observed plasticity in syndrome structure, within-population trait covariation patterns were remarkably consistent across latitudes, despite strong population-level divergence in trait means associated with local thermal adaptation. This consistency suggests that the trait associations may have acted as evolutionary constraints. If these phenotypic covariation patterns are underpinned by genetic correlations, they might constrain or facilitate future adaptive potential, for example in response to climate change, and this critically depending on the direction of the selection pressure.
Fast-lived low-latitude damselflies were found to be more sensitive to metal contamination than slow-lived high-latitude damselflies. There was also some evidence for a higher contaminant sensitivity in more fast-lived species, but not for a higher sensitivity to UV. These results indicate a potential coupling between POLS and stress sensitivity, yet more studies using a wider array of populations or species are needed to validate this pattern.
In conclusion, I documented an exceptionally large integrated set of life-history, behavioural and physiological traits and covariation patterns within the POLS framework and found the POLS hypothesis predicting trait associations along a unidimensional fast-slow axis of variation to be too simplistic to capture a complex reality. This study further provided a first exploration of how trait covariation patterns might be affected by global warming and pollution. My findings highlight the need for integrated multi-trait approaches, essential to understand and predict how organisms deal with current and future challenges.status: Publishe
Evolutionair-ecotoxicologische studie over de effecten van dagelijkse temperatuursfluctuaties op de toxiciteit van pesticiden in waterjufferlarven
No full textIn natural ecosystems animals encounter several environmental stressors that furthermore can interact with pollutants and potentially increase their toxicity. This is considered one of the underlying reasons why current ecological risk assessment is possibly failing to protect natural ecosystems as it may be lacking realism by being based on pesticide toxicity testing under standard laboratory conditions. While it is widely known that an increase in mean temperature increases the toxicity of pollutants, studies largely ignored the effects of daily temperature fluctuations (DTFs) on pesticide toxicity and never tested pollutant toxicity under both global warming stressors (the more realistic scenario in which both the mean temperature and the DTF increase). Furthermore, how DTFs shape pesticide toxicity is mostly unknown, which asks for an integrated approach including life history and physiology. In this thesis, I tested for the single and combined effects of exposure to the pesticide chlorpyrifos (CPF) and warming (+ 4 °C increase in mean temperature and a + 5 °C increase in DTF) in Ischnura elegans damselfly larvae by executing a series of common-garden experiments. I studied effects on life history traits, heat tolerance and candidate underlying physiological mechanisms. Thereby, I used damselfly larvae across a latitudinal gradient (European low- and high-latitude populations) to study the role of thermal adaptation in shaping the sensitivity to pesticides under global warming. The mean summer water temperatures and maximum summer DTFs in shallow freshwater ponds located in southern France (low latitude) are 24 °C with 10 °C DTF, and in southern Sweden (high latitude) are 20 °C with 5 °C DTF. This 4 °C difference in mean temperature and 5 °C difference in maximum DTF also matches the predicted increase in both factors by 2100 under the IPCC RCP 8.5 scenario, which allows for applying a space-for-time substitution to test if gradual thermal evolution in high-latitude populations may buffer for the increased pesticide toxicity under global warming (increase in both mean temperature and DTF). I reviewed the strengths and weaknesses of this approach in chapter I.
In the second chapter, I studied the effects of global warming in the absence of the pesticide and I found that DTFs only had negative effects on growth rate under the 4 °C warming treatment. While 4 °C warming was beneficial for larvae of both latitudes, this changed in a negative effect in the presence of high DTF. These negative effects of DTF were stronger in high-latitude larvae and already occurred at low DTF, indicating local thermal adaptation. This also suggests that if high-latitude populations are able to gradually thermally evolve into 'low-latitude' populations, they would no longer suffer a growth reduction in the presence of DTF under 4 °C warming.
When studying the effects of DTFs on pesticide toxicity in chapter III, I found the striking result that while the used chlorpyrifos concentration was not affecting the damselfly larvae's life history at a constant temperature of 20 °C, it did strongly decrease survival and growth in the presence of DTFs around 20 °C. These results suggest that in standard pesticide toxicity tests, which are carried out by current risk assessment, this concentration would have been regarded as safe. Thereby, this highlights it is crucial to integrate DTFs in current risk assessment to reach more realistic predictions about pesticide toxicity in natural systems.
In the last three chapters, I studied the effects of pesticides under global warming, thereby including the predicted increases in both mean temperature and DTF. The toxicity of chlorpyrifos was magnified by the increase in both mean temperature and DTF, but especially at their combination. Furthermore, I described in chapter V a novel, likely general mechanism that contributes to the higher chlorpyrifos toxicity under global warming by coupling two general principles: the widespread temperature-size rule and the size-pesticide sensitivity pattern. Larvae got smaller under DTFs, and these smaller larvae were more vulnerable to the pesticide, hence the higher chlorpyrifos toxicity under DTFs was partly mediated through DTF-induced reductions in body size. In terms of physiological variables, I found evidence of chlorpyrifos-induced effects being stronger under DTFs in terms of oxidative damage to lipids, which may contribute to the mortality patterns. Further, in my last chapter, I observed that the chlorpyrifos-induced reductions in bioenergetic response variables (energy availability and net energy budget) were stronger when the high mean temperature was combined with the high DTF. Moreover, I also showed that the bioenergetic responses contributed to the higher chlorpyrifos toxicity under global warming as treatment combinations with lower net energy budgets showed higher mortality and lower growth rates. Although I did not always find evidence that possible gradual thermal evolution in high-latitude damselflies would buffer for the increased chlorpyrifos toxicity under global warming, I did find a strong signal in chapter IV. Latitude-specific thermal adaptation to both mean temperature and DTF buffered for the chlorpyrifos-induced reduction in heat tolerance, meaning that possible gradual thermal evolution in high-latitude populations may buffer for the negative effects of chlorpyrifos on heat tolerance under warming, unless the DTF increase is taken into account.
My results indicate that it is crucial to not only consider DTFs, but also their interaction with increasing mean temperatures, and to integrate gradual thermal evolution to make more realistic predictions of pesticide toxicity in the current climate and in a warming world.status: Publishe
Gecombineerde effecten van biotische stressoren en pesticiden in aquatische insecten : van individu tot gemeenschap
No full textChapter I
Ecological relevance and sensitivity depending on the exposure time for two biomarkers
Biomarkers are widely used to assess pesticide stress, but their ecological relevance and exposure time dependent sensitivity is still heavily debated. We studied both aspects in larvae of the damselflystatus: Publishe
Eco-evolutionary dynamics during range expansion in a herbivorous arthropod
Full text linkThe earth’s climate has a history of alternating glacial and interglacial periods, which have recurrently forced major rearrangements in species assemblages. Today, however, scientists are worried because the predicted rate of climate change is faster than any of these past temperature changes, and anticipated to have dramatic consequences for the earth’s biodiversity. One way in which species may respond to the current global warming, is by shifting their range pole- or upwards. During such shifts, individuals encounter changing environmental conditions (like a shortened breeding season) and become assorted according to their dispersal capacities (best dispersers at the front). Range shifts thus entail strong selection pressures that may profoundly shape range front phenotypes. This PhD thesis studies the ecological and evolutionary processes related to range shifts, using the two-spotted spider mite (a herbivorous pest that recently expanded its European range northwards) as a model species
Biodiversiteit en structuur van poelgemeenschappen volgens een hydrologische gradiënt.
Full text linkDe bescherming van relatief kleine watersystemen zoals meertjes, vijvers en tijdelijke poelen is belangrijk om de integriteit en biodiversiteit van het veranderende Europese landschap te verzekeren. Deze habitatten onderhouden niet alleen de regionale biodiversiteit, maar doordat zijn instaan voor het bufferen van overstromingen en het verbeteren van de waterkwaliteit, kunnen ze ook van nut zijn voor de maatschappij. Enkel op basis van ecologische studies die peilen naar de werking van deze ecosystemen en de factoren die hun levensgemeenschappen structureren, kunnen efficiënte beheersmaatregelen voor deze waardevolle habitatten worden geformuleerd. Onze studie was voornamelijk gericht op ecologische processen die het voorkomen van ongewervelde sleuteltaxa verklaren in ruimte en tijd in een set van pristiene tijdelijke poelen in Kiskunság (Hongarije). We voerden een intensieve veldsurvey uit van de grote branchiopoden tijdens de lente van 2005 en 2006, en dit in een totaal van 82 poelen behorende tot vijf verschillende habitattypes (weidepoelen, kleiputten, karrensporen en poelen in akkers en boomgaarden). We bestudeerden lokale en ruimtelijke factoren die het voorkomen van de meest algemene soorten verklaarden. Om processen te bestuderen die de watervlooiengemeenschappen structureren, concentreerden we ons op een subset van 18 weidepoelen en kleiputten. Deze poelen, gesitueerd in drie poelclusters en met een variabele duur van de vullingfase (hydroperiode), werden opeenvolgend bemonsterd in de lente van 2005. Omwille van lage neerslaghoeveelheden tijdens de lente en voorgaande winter en relatief hoge lentetemperaturen in 2007, waren slechts vier poelen gevuld en konden bijgevolg worden bemonsterd. Bijkomend werd de dormante branchiopodengemeenschap (rusteierenbank) verzameld en in het laboratorium tot ontluiking gebracht om de soortenrijkdom verder in te schatten en ontluikingsvereisten van soorten te bestuderen.De hoge regionale soortenrijkdom en frequentie van voorkomen van grote branchiopoden, een taxon waarvan de bescherming internationaal als een hoge prioriteit wordt erkend, onderschrijven de natuurwaarde van de tijdelijke zoetwaterpoelen in Kiskunság. Onze studiepoelen behoorden verder tot de meest soortenrijke tijdelijke zoetwaterhabitatten met betrekking tot Cladocera in vergelijking met een totaal van 36 studies die wereldwijd werden uitgevoerd. We definieerden Kiskunság daarom als een hot spot zowel van kleine als grote branchiopoden en benadrukten het belang van hun bescherming. De hoge regionale branchiopodendiversiteit kwam tot stand door de hoge habitatdiversiteit. Variatie in de soortensamenstelling van de grote-branchiopodengemeenschappen was gerelateerd aan verschillen in lokale habitatkarakteristieken zoals grootte, helderheid en de graad van bedekking door vegetatie. Het significante effect van lokale habitatkarakteristieken vormde bovendien een aanwijzing voor species sorting als een belangrijk structurerend mechanisme van de metagemeenschappen van grote branchiopoden in onze studiepoelen. De mate waarin de ruimtelijke verspreiding van soorten het resultaat is van dispersielimitatie of ongekende omgevingsgradiënten blijft voorlopig onduidelijk. Een vergelijkende literatuurstudie gaf aan dat de hoge regionale soortenrijkdom aan watervlooien gerelateerd was aan de hoge graad van variatie in habitatgrootte en inundatieduur.De tijdelijke studiepoelen en hun levensgemeenschappen vertoonden variatie in de tijd. Tijdens het groeiseizoen nam de conductiviteit van het water toe en observeerden we groei van waterplanten en algen, die resulteerden in een hogere troebelheid. Naarmate de habitatkwaliteit veranderde, werden de watervlooiengemeenschappen gedomineerd door kleine soorten en/of soorten die doorgaans geassocieerd zijn met waterplanten. We vermoeden dat de aanwezigheid van relatief grote zooplanktontaxa zoals Daphnia en anostraken enkel vroeg in de successie, evenals hun kleine proportie in de branchiopodengemeenschappen van weidepoelen en kleiputten, in het algemeen te wijten was aan grootte-selectieve predatie. De hoge regionale soortenrijkdom aan watervlooien in Kiskunság in vergelijking met diverse studies wereldwijd werd gedeeltelijk ook toegewezen aan de relatief lange hydroperiode van de poelen. Zelfs in poelen die voor een vrij korte periode gevuld waren, was voor verscheidene soorten watervlooien immers voldoende tijd beschikbaar om hun levenscyclus te vervolledigen en was hun kolonisatiesucces daardoor niet beperkt. In poelen die vroeger opdroogden, kwamen tijdens een volledige vullingfase echter gemiddeld minder soorten voor omdat de seizoenaleopeenvolging en vervanging van soorten eerder werd onderbroken.Naast intraseizoenale variatie, bestudeerden we ook de interseizoenale variatie in de samenstelling van de watervlooiengemeenschap. Tijdens een droog jaar (2007) waren minder soorten watervlooien aanwezig in de poelen en slechts kleine populaties in vergelijking met het voorgaande natte jaar (2005). Indien de huidige trends van verminderde neerslag en toenemende droogte zich voortzetten in de toekomst, valt te verwachten dat poelen in Kiskunság op termijn gemiddeld kleiner zullen worden en voor kortere periodes gevuld zullen blijven. Hoewel tijdelijke-poelbewoners variatie in hun omgeving relatief goed kunnen tolereren, zijn ze mogelijk niet in staat om zich op lange termijn snel genoeg aan zulke veranderingen aan te passen. Niet alleen de verarming van de gemeenschappen in de kleinere poelvolumes tijdens het droge jaar, maar ook de onderbreking van seizoenale successie in poelen die eerder opdrogen, geeft aan dat de soortenrijkdom aan watervlooien negatief zou worden beïnvloed door zulke hydrologische veranderingen. Gezien watervlooien een belangrijke schakel zijn in de voedselketen van deze ecosystemen, kunnen wijzigingen in hun gemeenschappen nefaste gevolgen hebben voor de diversiteit op verschillende trofische niveaus en de ecologische waarde van deze ecosystemen.Aan de hand van gecontroleerde laboratoriumexperimenten observeerden we een soortspecifieke ontluikingsrespons van watervlooien op gecombineerde temperatuur- en fotoperiodebehandelingen waarbij maximale ontluikingsfracties voorkwamen onder condities die overeenkwamen met het moment in het seizoen waarop soorten in het veld ook een maximale abundantie vertoonden. Zulke respons wijst mogelijk op een mechanisme van temporele habitatselectie dat soorten in staat zou stellen om populaties op te starten voornamelijk wanneer ze verwacht worden een hoge relatieve fitness te hebben. Doorgaans wordt aangenomen dat ontluiking enkel bijdraagt tot het opstarten van actieve zoöplanktonpopulaties in het begin van het groeiseizoen. De respons die wij observeerden zou echter kunnen resulteren in een belangrijkere bijdrage van ontluiking tot seizoenale patronen in de actieve gemeenschappen.Tenslotte evalueerden we de efficiëntie van de identificatie van organismen ontloken uit rusteieren voor het inschatten van de lokale diversiteit aan watervlooien in onze studiepoelen. We maakten bovendien gebruik van resultaten uit het eerste hoofdstuk waarbij deze methode werd gebruikt om de soortenlijst van grote branchiopoden aan te vullen. In eerdere studies in permanente meren bleek deze methode efficiënt. Onze resultaten, in combinatie met eerdere studies in tijdelijke wetlands, gaven echter aan dat de methode niet even efficiënt is in alle types tijdelijke aquatische systemen. Vooral in ondiepe tijdelijk poelen vormt rusteierenbankanalyse een minder betrouwbare methode voor het inschatten van de lokale soortenrijkdom, terwijl in diepere tijdelijke systemen de methode betere resultaten gaf.Op basis van onze bevindingen formuleerden we enkele nuttige richtlijnen voor een duurzaam beheer van tijdelijke zoetwaterhabitatten. Om in de eerste plaats de lokale soortenrijkdom aan branchiopoden op een betrouwbare manier in te schatten zijn actieve stalen te verkiezen boven de identificatie van organismen ontloken uit ruststadia. Actieve stalen dienen verder bij voorkeur genomen te worden tijdens momenten gespreid in de tijd, zoals een vroege, midden en late vullingfase. Teneinde een hoge regionale diversiteit aan watervlooien en grote branchiopoden te bewaren, is een hoge habitatdiversiteit aangewezen, vooral met betrekking tot habitatgrootte, helderheid en bedekking met vegetatie. Verscheidene andere groepen aquatische organismen zijn waarschijnlijk ook gebaat bij zulke maatregel. Modderpoelen en karrensporen waren een voornaam habitat voor grote branchiopoden. Dergelijke habitatten die weinig aantrekkelijk lijken voor de mens en daardoor vaak verwaarloosd worden, dienen daarom bewaard te blijven in het landschap.status: Publishe
Multi-stressor ecotoxicologische studie op Culex muggen: van toxiciteitsmechanismen tot biotische interacties
No full textNatural populations are increasingly facing multiple stressors. Their ability to deal with interacting stressor combinations will be crucial for their local persistence. Populations of target species are typically exposed to pesticide mixtures and natural stressors, and are increasingly developing resistance to single pesticides. Nevertheless, we have poor knowledge whether natural stressors and the presence of pesticide resistance shape mixture toxicity. To assess the pesticide control efficiency and to reduce ecological damage to non-target species, it is important to quantify the effect of pesticide mixtures and compare them with the effect of their single pesticides on pest species, non-target species and their predator-prey interactions. Natural stressors that are widespread in freshwater systems are predation risk and warming; both may magnify the toxicity of single pesticides. The latter pattern has been captured in the 'Climate-induced toxicant sensitivity' concept (CITS). Nevertheless, deviations from this general pattern have been reported. To advance insights, there is a pressing need to identify the underlying molecular stress mechanisms of the CITS patterns. Moreover, while many studies on the toxicity of pesticides looked at the effects of a higher mean temperature, effects of the realistic scenario of daily temperature variation (DTV, which is a key component of global warming) are understudied. In this context, developmental stages and consequences for biotic interactions such as competition have also been largely ignored.
In Chapters 1-2 (Part I), I tested the single and combined effects of the pesticide chlorpyrifos and the biopesticide Bacillus thuringiensis israelensis (Bti) on the survival of a chlorpyrifos-resistant and non-resistant strain of the Southern house mosquito Culex quinquefasciatus. In Chapter 1, I investigated whether these effects of chlorpyrifos and/or Bti were magnified by synthetic predator cues of Notonecta water bugs. Single exposure to Bti caused mortality in both strains and single exposure to chlorpyrifos caused only mortality in the non-resistant strain, while predator cues did not induce mortality. The chlorpyrifos-resistant strain was more sensitive to Bti, indicating a cost of resistance. The interaction types between chlorpyrifos and Bti (additive), between chlorpyrifos and predator cues (additive), and between Bti and predator cues (additive) were consistent in both strains. In Chapter 2, I tested the effects of chlorpyrifos and/or Bti on the mortality by predation by the pygmy backswimmer Plea minutissima. After exposure to the mixture, equal mortality by predation was caused in both mosquito strains. As expected, less mortality by predation in the chlorpyrifos-resistant mosquito strain compared to the non-resistant strain occurred after the chlorpyrifos exposure. Notably, the predator killed more mosquito larvae of the resistant strain compared to the non-resistant strain after Bti exposure indicating a predation cost of resistance in the presence of a biopesticide. Part I highlights the integrated use of Bti and natural control by predators as a promising strategy to counter the build-up of resistance and to keep vector mosquito populations under control.
In chapters 3-5 (Part II), I tested whether daily temperature variation (DTV) magnifies the toxicity of chlorpyrifos in the Northern house mosquito Culex pipiens. In Chapter 3, I also studied whether DTV magnifies the single toxicity of Bti and/or its combined toxicity with chlorpyrifos. DTV was not lethal and did not change the toxicity of the individual pesticides. Yet, a key novel finding was that high DTV increased the mortality of the mixture by changing the interaction between both pesticides from additive to synergistic. In Chapter 4, I tested whether the effect of DTV and its interaction with chlorpyrifos was dependent on the developmental stage. DTV had again no direct negative effects and did not change the toxicity of the individual pesticides. Exposure to chlorpyrifos at a constant temperature-imposed mortality and reduced the heat tolerance in both larvae and adult males, but not in adult females. This pesticide-induced decrease of heat tolerance is in line with the TICS ("toxicant-induced climate change sensitivity") concept whereby the first evidence was provided that the TICS can be sex-specific. Notably, DTV interacted synergistically with chlorpyrifos for heat tolerance of the larvae and adult females. DTV increased the chlorpyrifos-induced decrease (CITS) of heat tolerance (TICS), providing support for the reciprocal effects between DTV and contaminants, hence the coupling of the TICS and CITS concepts (CITS --> TICS). This coupling of CITS and TICS was developmental stage specific as the interaction effect between DTV and chlorpyrifos was additive for adult males. In Chapter 5, I also studied the effect of competition with the water flea Daphnia magna on the combined effects of DTV and chlorpyrifos on the mosquito larvae. In this experiment, no pesticide-induced mortality was observed in the presence of DTV due to an accelerated pesticide breakdown under DTV, which contrasts with the general pattern of the CITS concept. There was neither a significant effect of competition on mortality, nor did competition influence the interaction between the single pesticide and DTV. Together these chapters underscore the importance to consider the effects of DTV on pesticide toxicity and on pesticide exposure in risk assessment of toxicants.
In Chapters 6-7 (Part III), I tested three concentrations of the pesticide chlorpyrifos (absence, low-effect and high-effect) in the absence and presence of 4 °C warming on larvae of the Northern house mosquito Culex pipiens. In Chapter 6, I showed that both the low-effect and high-effect chlorpyrifos concentrations were lethal and generated mostly negative sublethal effects: activity of acetylcholinesterase (AChE) and total fat content decreased, and oxidative damage to lipids increased, yet growth rate increased. Warming was slightly lethal, yet had positive sublethal effects: growth rate, total fat content and metabolic rate increased, and oxidative damage decreased. The independent action model identified the expected synergistic interaction between chlorpyrifos and warming in four out of seven response variables. Notably, three variables (survival, AChE, and fat content) were strongly dependent on the chlorpyrifos concentration, and two of these (AChE and fat content) were not associated with a significant interaction in the general(ised) linear models. In Chapter 7, I tested the effects of chlorpyrifos under warming at the gene expression level. By applying the independent action model on RNA-seq data I confirmed my hypothesis that synergistic interactions between both stressors at the phenotypic level are underpinned by a higher frequency or strength of antagonistic upregulations (less upregulated than expected based on responses to the single stressors) and of synergistic downregulations (more downregulated than expected) of general stress defence response genes (protection of macromolecules, antioxidant processes, detoxification, and energy metabolism/allocation).
These results are relevant to improve vector mosquito control strategies, resistance management and ecological risk assessment of pesticides. I identified a novel cost of resistance to a chemical pesticide in terms of increased vulnerability to a biopesticide, and to predation after exposure to the biopesticide. In addition, the finding of a higher toxicity of the mixture at high DTV compared to the typically used constant test temperatures in the laboratory urges caution when evaluating the environmental impact of pesticide mixtures. Not only the effects of DTV on pesticide toxicity, but also on pesticide degradation (hence exposure) should be considered in ecotox testing. I identified several factors that may affect the detection of the CITS concept: dependence on concentration, developmental stage, genetic strain and sex, and appropriate null model testing. The identified factors are important to take into account when studying the toxicity of contaminants in a warming world. Finally, I provide guidelines to formally test the stressor interaction type for gene expression data. Following this approach, my results highlight that a quantitative analysis of the frequency and strength of the interaction types of general stress response genes, specifically focusing on antagonistic upregulations and synergistic downregulations, may advance the mechanistic understanding of how other stressors modify the toxicity of contaminants.status: Publishe
The Gut Microbiome Causally Contributes to Interspecific Differences in Pesticide Sensitivity
No full textExplaining interspecific differences in pesticide sensitivity is key to increasing the predictive power of ecotoxicology. Besides species traits, the gut microbiome may provide an untested additional predictive factor since it often plays a role in host defense against stressors. Therefore, we investigated the gut microbiome's causal role in shaping differences in pesticide sensitivity between two congeneric damselfly species. After an antibiotic treatment, reciprocal gut microbiome transplants were performed between pesticide-sensitive Ischnura elegans and more tolerant Ischnura pumilio larvae, with donor larvae first preexposed to either chlorpyrifos or a solvent control to match the subsequent pesticide treatments of the recipients. The gut microbiome, determined by 16S rRNA gene amplicon sequencing, of both species included pesticide-degrading bacteria, but also showed shared and species-specific responses to the pesticide. Notably, the most pesticide-sensitive combination, with the highest pesticide-induced mortality, consisted of I. elegans larvae receiving I. elegans donor gut microbiota, whereas the least sensitive combination consisted of I. pumilio larvae receiving I. pumilio donor gut microbiota, whereby the pesticide did not increase larval mortality. The two mixed donor-recipient gut microbiome combinations resulted in an intermediate sensitivity. Remarkably, I. elegans recipient larvae experienced a lower chlorpyrifos-induced mortality when they received an I. pumilio donor gut microbiome than when they received their conspecific I. elegans donor gut microbiome. Our results provide, to our knowledge, the first proof-of-evidence that the gut microbiome causally contributes to species differences in pesticide sensitivity.Funding
Financial support came from research grants from KU Leuven (C16/17/002) and FWO-Flanders (G.095619 and G014423N).
ACKNOWLEDGMENTS
We thank Ria Van Houdt for analytical support, and Floortje Vleugels, Geert Neyens and Rony Van Aerschot for technical support during the experiment. C.T. and M.F. are Ph.D. fellows, and J.V. a postdoctoral fellow of FWO-Flanders, N.T. is a postdoctoral fellow of the Alexander von Humboldt foundatio
De evolutie van anti-predatorkenmerken bij de watervlo Daphnia magna: een functioneel-ecologische benadering.
No full textHet hoofddoel van deze thesis bestond erin het inzicht te veruimen in deevolutionaire ecologie van anti-predatie gedrag in de watervlo Daphniamagna. De ecologische context vanpredator-prooi interacties is reeds veel bestudeerd en veel aandacht hierbij isgegaan naar predator geïnduceerde morfologische-, gedrags- enlevensgeschiedenis kenmerken. In tegenstelling is nog maar weiniggeweten over fysiologische/biochemische veranderingen in respons op predatie. Doorde incorporatie van dergelijke kenmerken willen we een meer volledig beeldkrijgen van de verdedigingsmechanismen tegen predators. Hiervoor pasten we eendubbele strategie toe. Langs de ene kant hebben we gescreend voor fysiologischekenmerken die potentieel kunnen worden toegevoegd aan de set vanverdedigingsmechanismen die door Daphniaworden aangewend in respons op vispredatie. Langs de andere kant hebben wegebruik gemaakt van een proteomics benadering, waarbij we proteïnen hebben geïdentificeerddie differentieel tot expressie komen bij predatierisico. Behalve alseindpunten kunnen fysiologische/biochemische kenmerken ook onderliggende mechanismen blootleggen van reeds gekende verdedigingsmechanismen.Dit zal onze kennis verruimen van hoe prooien omgaan met predatie en hoemeervoudige verdedigingsstrategieën worden geïntegreerd. Om specifiek te kijkennaar de evolutie van fysiologische/biochemische kenmerken gerelateerd aanverdediging ten opzichte van natuurlijke vijanden, hebben we gebruik gemaaktvan een herrijzenis aanpak. We hebben het evolutionaire potentieel en hetevolutionaire traject gekwantificeerd van twee van de bestudeerde kenmerken, inD. magna afkomstig vandrie verschillende subpopulaties gescheiden in de tijd. Deze Daphnia zijn afkomstig van rusteierenuit verschillende diepten van een rusteierenbank van een natuurlijke vijver uitOud Heverlee. Omdat we de geschiedenis kennen van zowel de visbepotingen alsvan de parasitaire druk doorheen de tijd, zijn we in staat om dit tevergelijken met het expressie patroon van onze kenmerken te vergelijken. Hierdoorkunnen we de evolutionaire veranderingen van de populatie reconstrueren inrespons op de aanwezigheid van verschillende vijanden.In hoofdstuk 1 hebben we ons geconcentreerd op een specifieke fysiologischeindpunt: heatshock proteïne 60 (Hsp60), een belangrijk stress proteïne, datbetrokken is in de cellulaire verdediging. We hebben het effect vanviskairomonen getest op de hoeveelheid Hsp60, en konden een tijdelijke inductieaantonen na blootstelling aan predator stress. Dit suggereert dat Hsp60 wordtopgereguleerd in reactie op acute predator stress, zodat andereverdedigingsmechanismen kunnen ontwikkelen en de verdediging overnemen. Wevonden genetische variatie voor de inductie respons, zowel als voor deconstitutieve hoeveelheid aan Hsp60, gelinkt aan de natuurlijke habitatten vande clones en de residente vispredatie. In hoofdstuk 2 hebben we het aantalbetudeerde fysiologische kenmerken uitgebreid en getest in welke mate deresponse op predatie afhankelijk is van de voorradige energie (voedsel stress).Voedsel stress had een sterke invloed op alle bestudeerde kenmerken, terwijl deresponse op predatie in tegenstelling tot bij de levensgeschiedenis kenmerken,minder uitgesproken was voor de fysiologische kenmerken. Relatieve investeringin verdediging was hoger bij voedsel stress, terwijl als voedsel meer voorradigis, meer energie geïnvesteerd werd in reproductie. In de volgende tweehoofdstukken hebben we aangetoond dat de subpopulaties van ons studiesysteemeen sterk evolutionair potentieel had en hebben de evolutionaire veranderingenvan de hoeveelheid stress proteïnen Hsp60 (hoofdstuk 3) en de activiteit vanhet enzym profenoloxidase (proPO) (immuniteit: hoofdstuk 4) gereconstrueerd. Hsp60levels stegen gelijkmatig doorheen de tijd, parallel aan de stijging inparasitaire druk in de vijver, waardoor ze dus niet overeenkwamen met deveranderingen in vispredatie. Ook de proPO activiteit steeg doorheen de tijd,maar dit enkel tussen de oudste periode met een zeer lage densiteit aanparasieten en de daaropvolgende periode met een verhoogde parasieten druk. Naastvoor fototactisch gedrag, waar reeds een evolutionaire respons was beschreven,hebben we zeer snelle (5-10 jaar) microevolutie in een natuurlijke populatie aangetoondvoor zowel Hsp60 en proPO. Predatie en parasieten hebben in deze populatie eenzeer sterke selectie druk gevormd die evolutie veroorzaakt heeft in deverdedigingsmechanismen. In het laatste hoofdstuk (hoofdstuk 5), hebben we eenmethode geoptimaliseerd om proteïnen expressie profielen te vergelijken tussendieren die al dan niet werden blootgesteld aan predators. We hebben 30differentiële proteïnen tussen predator blootgestelde en controle dierengeïdentificeerd. Hoewel onze resultaten nog in een exploratief stadium zitten,hebben we reeds enkele interessante proteïnen gevonden, waarvan de functie isgerelateerd met energie opname en allocatie, gen regulatie, cytoskeletkarakteristieken, signaal transductie, en resistentie tegen hypoxia enparasieten.Alles bij elkaar toont het in deze thesis voorgestelde onderzoek aan datfysiologische/biochemische kenmerken, zowel als eindpunten als intermediairenin onderliggende processen, een extra inzicht kunnen bijbrengen over hoeprooien omgaan met predators en parasieten. De exploratieve proteomicsresultaten geven aan dat de ontwikkelde techniek veelbelovend zijn voor verderonderzoek naar hoe fysiologische kenmerken betrokken zijn in de onderliggendemechanismen van anti- predatie verdediging and de link met verdediging tenopzichte van andere stressoren.status: Publishe
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